1. Field of the Invention
The present invention relates to an electrophotographic apparatus, such as a laser printer or a digital copying machine, in which an image is recorded by scanning and exposing a light beam onto a body to be scanned in accordance with image information.
2. Description of the Related Art
A structure of an optical scanning device 101 of a conventional electrophotographic apparatus 100 will be described with reference to FIGS. 32A and 32B and FIGS. 33A and 33B.
The optical scanning device 101 is constituted by a light source 106 for emitting a light beam L containing information, a polygon mirror 124A for deflecting the light beam L emitted from the light source 106 toward a specified direction, an imaging lens system 122 for imaging an image of the light beam L on a body 108 to be scanned such as a photosensitive drum, an optical box 109 housing the respective parts, and the like. Incidentally, the optical box 109 is provided with a window part 104 through which the light beam L passes.
The optical box 109 is closed by a cover 110 and is fixed to an optical scanning device mount frame 102 of the electrophotographic apparatus 100 by screws 107.
Further, tongue parts 105 of the optical scanning device mount frame 102 are inserted in not-shown side frames of the electrophotographic apparatus, and the optical scanning device mount frame 102 is positioned and fixed to the side frames with high accuracy.
The electrophotographic apparatus 100 causes the light beam L containing the information to main-scan the body 108 to be scanned so that an electrostatic latent image of the information is formed.
The electrophotographic apparatus 100 is constituted by a not-shown charging unit which uniformly charges the body 108 to be scanned, a developing unit which forms a toner image after the electrostatic latent image is formed by exposure from the main-scanning of the light beam L, a paper handling unit which synchronizes with the toner image and conveys a recording paper, a fixing unit, a frame for housing the respective units, and the like. The frame is generally formed such that two side frames are made to face each other, the optical scanning device mount frame 102 is supported at both ends and is fixed like a bridge, and a driving device for driving the body 108 to be scanned and the like is fixed to the side frames.
The conventional electrophotographic apparatus 100 has a problem that the vibration of the internal paper handling unit and the not-shown driving device for driving the body 108 to be scanned is transmitted to the optical scanning device mount frame 102 to vibrate the optical scanning device 101, so that deviation from a normal laser light path occurs to cause a scanning line deviation, and image quality becomes poor. Thus, as shown in FIG. 32B which is a view of FIG. 32A viewed in a direction of an arrow Y, a support part of the optical scanning device 101 is placed apart from a bent part 103 of the rectangular optical scanning device mount frame 102 facing the body 108 to be scanned by a predetermined value in view of the relation of S1≅S2. Accordingly, as shown in FIG. 32B, even if the optical scanning device mount frame 102 is vibrated, a change amount δ of the light beam L with respect to the body 108 to be scanned is very small. This is introduced in, for example, patent document 1 (JP-A-5-103164).
In an electrophotographic apparatus 120 of another example shown in FIGS. 34A to 34C, an optical scanning device 121 is of a type including a reflecting mirror 127, and a mount frame supported by an electrophotographic apparatus frame 133 is divided into an optical scanning device mount frame 129 and a reflecting mirror mount frame 130.
Incidentally, in FIGS. 34A to 34C, reference numeral 122 denotes an imaging lens system; 123, a light source; 124A, a polygon mirror; 124, a motor for rotating the polygon mirror; 125, an optical box; 126, a window part; 127, a reflecting mirror; 128, an attachment part; 129, an optical scanning device mount frame; 130, a reflecting mirror mount frame; 131, tongue parts; 132, attachment holes in which the tongue parts 131 are inserted; and 133, an electrophotographic apparatus frame.
By adopting the structure as stated above, since vibration of the motor 124 is not easily transmitted to the reflecting mirror 127, the improvement of image quality is achieved, and this is introduced in, for example, patent document 2 (JP-UM-A-3-39753).
Further, in an electrophotographic apparatus 140 of another example shown in FIGS. 35A and 35B, an optical scanning device 141 is provided with support parts 148 at four corners of an optical box 145, and is fastened to an optical scanning device mount frame 149 by only one screw 153 at a substantially center position of the four support parts.
Incidentally, in FIGS. 35A and 35B, reference numeral 142 denotes an imaging lens system; 143, a light source; 144, a motor for rotating a polygon mirror; 146, a window part; 147, a cylinder lens; 150, a boss; 151, a synchronous light reflecting mirror; 152, a synchronous light detection unit; and 154, a body to be scanned.
That is, even if a bottom plate of the optical box 145 is warped, it is forcibly pressed to the optical scanning device mount frame 149, and vibration is suppressed by fixing the bottom plate of the optical box 145 which is apt to vibrate, so that the improvement in the image quality can be achieved, and this is introduced in, for example, patent document 3 (JP-A-10-213768).
Besides, in an optical scanning device 160 of an electrophotographic apparatus of another example shown in FIGS. 36A and 36B, a reflecting mirror 161 is pressed by elastic bodies 165A, and a reflection plane 162 is pressed to support parts 164A, 164B and 164C of support bodies 163A and 163B.
Further, in the support body 163A for supporting the reflection plane 162 at one point of the support part 164A, support parts 164D and 164E separated from the reflection plane 162 by a clearance X are provided at both sides of the support part 164A, and an adhesive (not shown) is applied to the support parts 164D and 164E and the reflection plane 162.
By this, it is possible to prevent rotational vibration in directions of arrows E and F shown in FIG. 36D in the case where the reflecting mirror 161 is supported by three points of 164A, 164B and 164C of support bodies 163A and 163B as shown in FIG. 36C, and this is introduced in, for example, patent document 4 (JP-A-11-187224).
Incidentally, in many cases, a beam of an optical source of an optical scanning device is incident on a plane obliquely with respect to a motor.
Besides, fixing of the periphery of the light source must be devised so that a light source portion is not easily subjected to the influence of vibration.
In the electrophotographic apparatus 100 of FIGS. 32A and 32B and FIGS. 33A and 33B (JP-A-5-103164), as shown in FIG. 33A, the optical box 109 is fixed to the optical scanning device mount frame 102 by the screws 107 at the four positions apart from the bent parts 103 by S1 and S2, and since a portion of the optical box 109 close to a position Ea surrounded by a circle is fixed by the screw 107 at the position apart from the bent part 103 by S2, there is no problem. However, since a portion of the optical box 109 close to a position Eb surrounded by a circle (close to the light source 106), in which the respective optical parts are housed, must be formed firmly, it is necessary to enlarge the size of the periphery of the optical box 109 close to the position Eb.
Thus, a harmful influence is exerted on the miniaturization of the electrophotographic apparatus 100.
For example, although the portion close to the position Eb apart from the bent part 103 by S3 has only to be fixed by the screw 107, since the position Eb is near to the antinode of vibration shown in FIG. 33B, the light source portion is fluctuated by the vibration, the light path is deviated to L′, and an influence is exerted on the image quality.
Besides, in the electrophotographic apparatus of FIGS. 34A and 34B (JP-UM-A-3-39753), as shown in FIG. 34B, with respect to the fixing of the optical scanning device mount frame, it is fixed at two points on one side and at one point on the other side with respect to the center of the frame in the scanning direction. However, when attention is paid to a region Ec close to the light source, since the frame on the light source side and on the one point fixing side is vibrated as shown in FIG. 34C, the light beam L is deviated like L′, and an influence is exerted on the image quality.
Further, in the electrophotographic apparatus of FIGS. 35A and 35B (JP-A-10-213768), since the portion close to the center of the optical scanning device 141, which becomes the antinode, is fixed, it must be made firm so that the optical scanning device mount frame 149 does not vibrate, and therefore, the weight of the electrophotographic apparatus is increased and the cost is raised.
Besides, in the optical scanning device mount frame as shown in FIGS. 32A and 32B and FIGS. 33A and 33B (JP-A-5-103164), since the maximum deformation part at the time of vibration exists at the substantially center part of the optical scanning device mount frame, the technique of the optical scanning device of FIGS. 35A and 35B (JP-A-10-213768) can not be applied.
Besides, in the example of FIGS. 36A and 36B (JP-A-11-187224), since the adhesive is applied to the support parts of the reflecting mirror (reflection plane in the vicinity of the scanning region), it is necessary to take care not to erroneously apply the adhesive to the scanning region, and the application operation has been difficult.